Our specific aims are to elucidate fundamental correlates between structure and function for the enzyme ribulose bisphosphate carboxylase/oxygenase (RuBisCO) which catalyzes primary carbon dioxide fixation in nature and is one of the most abundant proteins on earth. This protein, which consists of large (L) and small (S) subunits in most species, undergoes activation to a catalytically active form which can then either catalyze carboxylative or oxygenolytic cleavage of ribulose bisphosphate. The latter initiates photorespiration, a process which opposes growth on carbon dioxide. Our long-range objective is to test the feasibility of enhancing photosynthesis and/or decreasing photorespiration by altering RuBisCO. The achievement of these objectives could increase crop yields and the global food supply. Our emphasis for many years has been on RuBisCO from bacteria. Bacteria not only provided enzymes that vary in quaternary structure (some lacking the S subunit) but one of the bacterial enzymes may be membrane-bound. A more basic understanding of enzyme structure and function and enzyme-membrane interactions may contribute to better treatment of a number of human diseases arising from enzyme or membrane malfunction. Specifically, we aim to investigate the structure and function of RuBisCO in terms of: (1) The function of S subunits including the interaction domain for L and S subunits and (2) the function of L subunits. These investigations will include chemical linking studies and in vitro mutagenesis of L and S subunit genes and will focus on one of the cyanobacteria, Anacystis nidulans. Parallel studies of the transformation of A. nidulans and cloroplasts by Co1E1 plasmids will be conducted to test the feasibility of incorporating interesting modifications of L and S subunit genes into cyanobacteria and, ultimately, into plants.